1. Field
The present disclosure relates generally to phased array antennas, and in particular, to phase shifters used with phased array antenna. Still more particularly, the present disclosure relates to a method and apparatus for electronically compensating for bit toggle errors associated with n-bit phase shifters to improve beam steering accuracy.
2. Background
As used herein, a “phased array antenna” is an array of antenna elements that may be used to direct a beam of electromagnetic radiation in a particular angular direction relative to the array of antenna elements. The array of antenna elements may include, for example, hundreds, thousands, or some other number of antenna elements arranged in an array. Each of these antenna elements may be capable of converting an electrical signal into electromagnetic radiation and/or converting electromagnetic radiation into an electrical signal.
The beam of electromagnetic radiation formed by an array of antenna elements may be directed, or steered, by controlling the phases applied to the electrical signals received and/or formed by the array of antenna elements. Typically, these phases are controlled using phase shifters. With currently available phased array antennas, digital phase shifters are most commonly used. A digital phase shifter provides a discrete set of phase states. Each phase state may correspond to a phase shift that may be applied to an electrical signal. The phase shift may be any phase angle between about 0 degrees and about 360 degrees. The set of phase states provided may be controlled by a group of bits. Each bit may be toggled between a bit value of “0” and a bit value of “1.” The bit values for the different phase bits may together form a binary configuration for the phase shifter. Each possible binary configuration may correspond to a particular phase state. In this manner, the number of possible phase states may be determined by the number of bits. With n bits, 2^n phase states may be provided.
When electronically steering the beam of electromagnetic radiation formed by an array of antenna elements, each phase shifter associated with an antenna element may be commanded to switch to a particular binary configuration to achieve a desired phase shift. However, the resulting phase shift may be different from the desired phase shift. This resulting phase shift may include a quantization error and a bit toggle error.
For example, the desired phase shift for a particular antenna element may fall between two discrete phase states. The difference between the desired phase shift and the phase shift indicated by the closest of the two phase states may be referred to as the quantization error. Further, toggling one or more bits for the phase shifter to change the binary configuration for the phase shifter between bit values may also introduce an error, which may be referred to as the bit toggle error.
The quantization errors and bit toggle errors associated with the phase shifters of a phased array antenna may reduce the accuracy with which the beam of electromagnetic radiation may be steered. Therefore, it would be advantageous to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.